1. Field of the Invention
The present invention relates to a method of preparing a toner and a toner prepared by the method. More particularly, the invention is directed to a method of preparing a toner using latex particles, and the resulting a toner. The invention is further directed to an image forming method using the toner and an image forming apparatus employing the toner.
2. Description of the Related Art
In an electrophotographic process or an electrostatic recording process, a developer is used to form an electrostatic image or an electrostatic latent image. The developer can be a two-component developer formed of a toner and carrier particles or a one-component developer formed of a toner only, without carrier particles. The one-component developer may be a magnetic one-component developer or a nonmagnetic one-component developer. Plasticizers such as colloidal silica are often added independently into the nonmagnetic one-component developer to increase the flowability of the toner. Generally, coloring particles obtained by dispersing a colorant, such as carbon black, or other additives in a binding resin are used in the toner.
Methods of preparing toners include pulverization or polymerization. In the pulverization method, the toner is obtained by melt mixing synthetic resins with colorants and, if needed, other additives, pulverizing the mixture and classifying the particles until a desired size of particles is obtained. In the polymerization method, a polymerizable monomer composition is manufactured by uniformly dissolving or dispersing a polymerizable monomer, a colorant, a polymerization initiator and, if needed, various additives such as a cross-linking agent and an antistatic agent. Next, the polymerizable monomer composition is dispersed in an aqueous dispersive medium which includes a dispersion stabilizer using an agitator to form minute liquid drop particles. Subsequently, the temperature is increased and suspension polymerization is performed to obtain a polymerized toner having coloring polymer particles of a desired size.
In an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus, an electrostatic latent image is formed through light exposure on the surface of a uniformly charged photoconductor. A toner is attached to the electrostatic latent image, and a resulting toner image is transferred to a transfer medium such as a paper through several processes such as heating, pressing, solvent steaming, etc. In most fixing processes, the transfer medium with the toner image passes through fixing rollers and pressing rollers, and by heating and pressing, the toner image is fused to the transfer medium.
Improvements in preciseness and minuteness are required for images formed by an image forming apparatus such as an electrophotocopier. Conventionally, a toner used in an image forming apparatus is usually obtained using pulverization of the toner material. When using pulverization, coloring particles with a wide range of particle sizes may be formed. Hence, to obtain satisfactory developer properties, there is a need to classify the coloring particles obtained through pulverization according to size to narrow the particle size distribution. However, it is difficult to precisely control the particle size distribution using a conventional mixing/pulverizing process in the manufacture of toner particles suitable for an electrophotographic process or electrostatic recording process. Also when preparing a minute particle toner, the toner preparation yield is low due to a classification process. In addition, there is a limit to the amount of change/adjustment of a toner design for obtaining desirable charging and fixing properties. Accordingly, polymerized toners, in which the size of particles is easy to control and which do not need to go through a complex manufacturing process such as classification, have come into the spotlight recently.
When a toner is prepared using polymerization, the desired size distribution of particles is obtained without performing pulverization or classification.
U.S. Pat. No. 6,033,822 in the name of Hasegawa et al. discloses a polymerized toner including a core formed of colored polymer particles and a shell covering the core in molecules, wherein the polymerized toner is prepared by suspension polymerization. However, it is still difficult to adjust the shape of the toner and the sizes of the particles using the process. Also, the particle size distribution is wide.
U.S. Pat. No. 6,258,911 in the name of Michael et al. discloses a bi-functional polymer having a narrow polydispersity and an emulsion-condensation polymerization process for manufacturing a polymer having covalently bonded free radicals on each of its ends. However, even when this method is used, a surfactant can cause an adverse effect, and it is difficult to control the size of latex.